D. Jaque

Nd3+ ion based self frequency doubling solid state lasers

Abstract Spectral and laser properties of three non-linear crystals (LiNbO3, LaBGeO5 and YAl3(BO3)4) activated with Nd3+ ions have been investigated. The main laser parameters (absorption and emission cross section, radiative lifetime and quantum efficiency) are determined and compared by means of optical spectroscopy. Optical spectroscopy is also used to estimate losses due to second harmonic (SH) self-absorption, energy transfer, excited state absorption and non-equivalent Nd centres. Continuous wave laser properties of the crystals in the fundamental and SH wavelengths are investigated under similar cavity geometry and pumping conditions using a tunable Ti–sapphire pump laser.

Compact, highly efficient ytterbium doped bismuthate glass waveguide laser

Laser slope efficiencies close to the quantum defect limit and in excess of 78% have been obtained from an ultrafast laser inscribed buried channel waveguide fabricated in a ytterbium-doped bismuthate glass. The simultaneous achievement of low propagation losses and preservation of the fluorescence properties of ytterbium ions is the basis of the outstanding laser performance.

Thermally resistant waveguides fabricated in Nd:YAG ceramics by crossing femtosecond damage filaments

We report on femtosecond laser writing of channel waveguides in Nd(3+) ion doped YAG ceramics by multiple inscriptions of damage filaments. Waveguiding between filaments was found to resist annealing temperatures as high as 1500 degrees C. Microluminescence imaging experiments have been carried out to elucidate the potential application of the obtained waveguides as integrated laser sources as well as to elucidate the waveguiding mechanisms.

Self-frequency-summing NYAB laser for tunable blue generation

Abstract Pulsed tunable blue laser light has been obtained in the 436–443 nm range by self-frequency summing the pump beam and the infrared laser beam produced by a nonlinear NYAB crystal. Excitation spectra of the blue emission are given. A theoretical model is developed and predicts the role of the different physical parameters.

Microstructuration induced differences in the thermo-optical and luminescence properties of Nd:YAG fine grain ceramics and crystals

The temperature and compositional dependences of thermo-optical properties of neodymium doped yttrium aluminum garnet (YAG) crystals and fine grain ceramics have been systematically investigated by means of time-resolved thermal lens spectrometry. We have found that Nd:YAG ceramics show a reduced thermal diffusivity compared to Nd:YAG single crystals in the complete temperature range investigated (80-300 K). The analysis of the time-resolved luminescent properties of Nd(3+) has revealed that the reduction in the phonon mean free path taking place in Nd:YAG ceramics cannot be associated with an increment in the density of lattice defects, indicating that phonon scattering at grain boundaries is the origin of the observed reduction in the thermal diffusivity of Nd:YAG ceramics. Finally, our results showed the ability of the time-resolved thermal lens to determine and optimize the thermo-optical properties of Nd:YAG ceramic based lasers.

Femtosecond-laser inscribed double-cladding waveguides in Nd:YAG crystal: a promising prototype for integrated lasers

We report on the design and implementation of a prototype of optical waveguides fabricated in Nd:YAG crystals by using femtosecond-laser irradiation. In this prototype, two concentric tubular structures with nearly circular cross sections of different diameters have been inscribed in the Nd:YAG crystals, generating double-cladding waveguides. Under 808 nm optical pumping, waveguide lasers have been realized in the double-cladding structures. Compared with single-cladding waveguides, the concentric tubular structures, benefiting from the large pump area of the outermost cladding, possess both superior laser performance and nearly single-mode beam profile in the inner cladding. Double-cladding waveguides of the same size were fabricated and coated by a thin optical film, and a maximum output power of 384 mW and a slope efficiency of 46.1% were obtained. Since the large diameters of the outer claddings are comparable with those of the optical fibers, this prototype paves a way to construct an integrated single-mode laser system with a direct fiber-waveguide configuration.

Cr3+→Nd3+ energy transfer in the YAl3(BO3)4 nonlinear laser crystal

The energy transfer between Cr3+ and Nd3+ ions in Cr3+, Nd3+:YAl3(BO3)4 (YAB) codoped crystals has been investigated by means of steady-state and time-resolved laser spectroscopies. The mainly nonradiative character of the energy transfer has been evidenced from the comparison between the emission spectra and the donor fluorescence decays. The analysis of the donor decay profiles has been used to determine the main dipole–dipole character of the transfer, in excellent agreement with the predictions made from the Dexter [J. Chem Phys. 21, 836 (1953)] model, as well as with the dependence of the energy-transfer rates on the acceptor concentration. The temperature behavior of the transfer rate has been analyzed considering the thermal-induced population redistribution between the E2 and T24 states of Cr3+ ions and the existence of the phonon-assisted energy transfer. We have obtained that 80% of the Cr3+→Nd3+ energy transfer in YAB is taking place without the assistance of lattice phonons whereas almost 20% ...

Luminescence of Rare Earth Ions in Strontium Barium Niobate Around the Phase Transition : The Case of Tm3+ Ions

The photoluminescence of ferroelectric Sr 0.6 Ba 0.4 (NbO 3 ) 2 congruent crystals doped with four different trivalent rare earth ions, Nd 3+ , Eu 3+ , Tm 3+ and Yb 3+ , has been examined in the temperature range around the Curie temperature, when the system undergoes the transition to the paraelectric phase. While the luminescence of large ions is not sensitive (Nd 3+ ) or weakly sensitive (Eu 3+ ) to the phase transition, that of small ions (Tm 3 + and Yb 3 + ) is highly sensitive to temperature changes around the Curie temperature. Particular emphasis is given to the Sr 0.6 Ba 0.4 (NbO 3 ) 2 :Tm 3 + system, for which the luminescence spectra around the phase transition and low temperature laser site selective spectra are systematically investigated. The different spectral sensitivity of the rare earth ions to the phase transition is interpreted in terms of the lattice sites occupied by the different rare earth ions in the Strontium Barium Niobate crystal host.

The effect of Nd and Mg doping on the micro-Raman spectra of LiNbO3 single-crystals

The LiNbO(3) congruent crystals doped with small Nd concentrations, <1xa0mol% Nd, and co-doped with Mg ions, 0-9xa0mol% Mg, were systematically investigated by means of micro-Raman spectroscopy in the Y and Z crystal directions. Results obtained from an undoped congruent crystal, an Nd-doped crystal, a Mg-doped crystal and Nd, Mg-co-doped crystals are compared. From the analyses of the results obtained in the Y direction, the Nd and Mg content dependence of the two lowest-Raman A(1)(TO(1)) and A(1)(TO(2)) modes, the half-width composition and the area ratio of the A(1)(TO(4)) and E(TO(8)) bands, we reached several conclusions about the incorporation mechanism of the Nd and Mg ions into the LiNbO(3) lattice. Likewise the Raman shift and half-width of the E(TO(1)) and E(TO(7)) modes were investigated in the Z direction. Results indicate that Mg and Nd ions are located in the Li site for low doping concentrations and for larger concentrations there is a replacement in both Li and Nb ion sites.

Effects of neodymium incorporation on the structural and luminescence properties of the YAl3(BO3)4?NdAl3(BO3)4 system

The luminescence of Nd(3+) ions in Nd(x)Y(1-x)Al(3)(BO(3))(4) (Nd:YAB) single crystals has been investigated as a function of the neodymium concentration in order to evidence the relation between the structural and spectroscopic properties in this nonlinear laser system. The analysis of the experimental data allowed us to individuate four different composition ranges. For moderate concentrations (x<0.2) the lattice parameters are nearly constant, and the emission spectra arise from Nd(3+) ions in unperturbed crystal sites. For concentrations in the 0.2<x<0.75 range the lattice parameters notably depend on the neodymium content, and a concomitant variation of the luminescence features is observed. In the 0.75<x<0.9 range a hexagonal to monoclinic phase transition takes place: the structural disorder is evidenced well by the broadening of the emission lines and by discontinuities in the concentration behaviour of other indicators such as the crystal-field strength, energy transfer parameters, etc. Finally, for x>0.9 the final formation of the NdAl(3)(BO(3))(4) (NAB) monoclinic phase is complete, and a new local ordering around Nd(3+) is very evident in the spectral features.